Fabric, paleomagnetism, and interpretation of pre-illinoian diamictons and paleosols on Cloudy Ridge and Milk River Ridge, Alberta and Montana

Abstract

Pebble fabrics and sedimentological properties indicate that pre-Wisconsinan diamictons (Kennedy Drift) on Cloudy Ridge (Alberta) and Milk River Ridge (Montana) are of glacial rather than colluvial origin. S1 and S3 eigenvalues of the upper units on the two ridges are typical of undeformed lodgement till whereas those of the lower unit on Milk River Ridge are typical of glacigenic sediment flow. Other properties, including compact matrices, striations on stones, mean pebble dip angles, and Schmidt equal-area stereonet patterns, suggest each unit is lodgement or basal till. Pedogenic features indicate weathering zones capping the tills are paleosols. Degree of rubification, clay, iron and aluminum buildup, and clay mineral alteration resembles those of very strongly developed soils formed in warmer and moister environments. The argument that “soil-like features” of the Cloudy Ridge unit resulted from post-burial diagenesis is disproven because nearly identical paleosols occur at the surface on Milk River Ridge and other interfluves to the south. Each unit examined has normal polarity. Based on comparisons with similar till/paleosol sequences exposed in Kennedy Drift sections on nearby interfluves, the Cloudy Ridge till and the upper till on Milk River Ridge were probably deposited during the early to middle Bruhnes Normal Chron (780 ka to present) whereas the lower till on Milk River Ridge is of earlier Brunhes age or dates back to the Olduvai (1.98 to 1.76 Ma) Normal Subchron or the Gauss Normal Chron (3.6 to 2.6 Ma).

Map showing spatial and temporal relations of mountain and continental glaciations on the Northern Plains, primarily in northern Montana and northwestern North Dakota

“…The intensely weathered diamicton in some places possibly is nonglacial alluvium; in some other places possibly it is till or alluvium overlain by till. Two pebble fabric measurements indicated to Karlstrom (Karlstrom, 2000b;Karlstrom and Barendregt, 2001) that the sediment he sampled is till. His till 1, till 2, and till 3 have reversed remanent geomagnetic polarity (Cioppa and others, 1995).…”

“…The temporal relation of till 1 to the oxygen isotope record is problematic. Karlstrom and Barendregt (2001) indicated that till 4 has normal remanent polarity. However, according to Cioppa and others (1995), the buried soil in till 4 has normal polarity, but the polarity of till 4 was not determined.…”

“…That reversal, possibly recorded in till and glacial lake sediments in Minnesota, Wisconsin, Missouri, and Iowa, occurred during oxygen isotope stage 82 (Sarnthein and Teidemann, 1990). Karlstrom and Barendregt (2001) stated that till 4 has normal remanent polarity. However, according to Cioppa and others (1995), the paleosol in the till has normal polarity but the polarity of the unaltered till was not determined.…”

“…1), a bedrock erosion surface remnant in Montana (Karlstrom, 1981(Karlstrom, , 1988a. Both of the diamictons were interpreted to be lodgement tills on the basis of pebble fabric analysis (Karlstrom and Barendregt, 2001). However, interpretation of the fabric from till 1 was not definitive.…”

Surface macro‐fabric analysis of relict rock glaciers in the Cantabrian Mountains (NW Spain)

“…36 In that sense, macro-fabric analysis focusses on the visible features of the coarse fraction of the sediments. [37][38][39][40] This technique has been used in different kinds of sediments, mainly glacial, [41][42][43][44][45][46][47][48][49][50] periglacial [51][52][53] and slope 54,55 deposits. Macro-fabric analyses have been performed to distinguish between different types of deposits such as mudflows and till, 56 different types of slope deposits, 57 rock glaciers and other periglacial landforms such as protalus ramparts 58,59 or landslides, scree and moraines.…”